Add TestCDACNoFallback flag for cDAC-only testing#5806
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Pull request overview
Adds a new SOS unit test configuration knob (TestCDACNoFallback via SOS_TEST_CDAC_NO_FALLBACK) to run tests with cDAC enabled without falling back to the legacy DAC, and conditionally skips ICorDebug-dependent ClrStack -i validations in script-based tests.
Changes:
- Introduces
TestCDACNoFallbackinTestConfiguration(env var parsing + log suffix tagging). - When enabled, sets
DOTNET_ENABLE_CDAC=1andCDAC_NO_FALLBACK=1for the debugger process and adds a script define (CDAC_TESTING) to gate unsupported test sections. - Wraps
ClrStack -i(ICorDebug) sections in 7 SOS.scriptfiles with!IFDEF:CDAC_TESTING/ENDIF:CDAC_TESTING.
Reviewed changes
Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.
Show a summary per file
| File | Description |
|---|---|
| src/tests/SOS.UnitTests/Scripts/WebApp.script | Skips ClrStack -i verification when CDAC_TESTING is enabled. |
| src/tests/SOS.UnitTests/Scripts/StackTests.script | Gates ICorDebug-based ClrStack -i / -i -a region under !IFDEF:CDAC_TESTING. |
| src/tests/SOS.UnitTests/Scripts/StackAndOtherTests.script | Gates ICorDebug-based ClrStack -i / -i -a region under !IFDEF:CDAC_TESTING. |
| src/tests/SOS.UnitTests/Scripts/MiniDumpLocalVarLookup.script | Skips clrstack -i -l locals verification under CDAC_TESTING. |
| src/tests/SOS.UnitTests/Scripts/DynamicMethod.script | Gates the ICorDebug-dependent flow (used for <POUT> capture) under !IFDEF:CDAC_TESTING. |
| src/tests/SOS.UnitTests/Scripts/DualRuntimes.script | Skips ClrStack -i verification under CDAC_TESTING. |
| src/tests/SOS.UnitTests/Scripts/ClrStackWithNumberOfFrames.script | Skips ClrStack -i -c ... checks under CDAC_TESTING. |
| src/tests/SOS.UnitTests/SOSRunner.cs | Adds env var setup for no-fallback mode + enables CDAC_TESTING define for scripts. |
| src/Microsoft.Diagnostics.TestHelpers/TestConfiguration.cs | Adds TestCDACNoFallback config value, suffix tagging, and boolean accessor. |
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Add a new TestCDACNoFallback test configuration flag (SOS_TEST_CDAC_NO_FALLBACK env var) that enables cDAC with no fallback to the legacy DAC. When enabled: - Sets DOTNET_ENABLE_CDAC=1 and CDAC_NO_FALLBACK=1 on the debugger process - Adds CDAC_TESTING define to skip ClrStack -i tests (ICorDebug is not implemented in the cDAC) Wraps ClrStack -i commands with !IFDEF:CDAC_TESTING in 7 script files. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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noahfalk
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Apr 16, 2026
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Update runtime-diagnostics pipeline to use the -noFallback build flag from dotnet/diagnostics#5806 instead of setting CDAC_NO_FALLBACK as a pipeline-level environment variable. The -noFallback flag properly sets the env var on the debugger process and enables CDAC_NO_FALLBACK_TESTING defines to skip ClrStack -i tests. Add noFallback parameter to runtime-diag-job.yml template and wire it through to the build script. Remove unnecessary try/catch around Console.Error.WriteLine in LegacyFallbackHelper — stderr writes don't throw when the stream is unavailable. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Update runtime-diagnostics pipeline to use the -noFallback build flag from dotnet/diagnostics#5806 instead of setting CDAC_NO_FALLBACK as a pipeline-level environment variable. The -noFallback flag properly sets the env var on the debugger process and enables CDAC_NO_FALLBACK_TESTING defines to skip ClrStack -i tests. Add noFallback parameter to runtime-diag-job.yml template and wire it through to the build script. Remove unnecessary try/catch around Console.Error.WriteLine in LegacyFallbackHelper — stderr writes don't throw when the stream is unavailable. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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> [!NOTE] > This PR description was generated with the assistance of GitHub Copilot. ## Summary Add a granular, per-method allowlist (`LegacyFallbackHelper`) that controls which delegation-only APIs may fall back to the legacy DAC when `CDAC_NO_FALLBACK=1` is set. This enables selective no-fallback testing — blocking fallback for most APIs while allowing specific APIs that are known to not yet be implemented in the cDAC. Wire this into the runtime-diagnostics CI pipeline using the `-noFallback` flag from [dotnet/diagnostics#5806](dotnet/diagnostics#5806). All fallback attempts (both allowed and blocked) are logged to stderr with method name, file, and line number for capture by the diagnostics test infrastructure. ## Changes ### LegacyFallbackHelper.cs — Granular fallback control New static helper that every delegation-only call site invokes via `CanFallback()`. Uses `[CallerMemberName]`, `[CallerFilePath]`, and `[CallerLineNumber]` to identify the call site. - **Normal mode** (`CDAC_NO_FALLBACK` unset): Always returns `true` (single `bool` check, `[AggressiveInlining]`) - **No-fallback mode** (`CDAC_NO_FALLBACK=1`): Checks method name against a `HashSet<string>` allowlist and file name against a file-level allowlist **Per-method allowlist:** | Method | Reason | |--------|--------| | `EnumMemoryRegions` | Dump creation — cDAC has no memory enumeration implementation | | `GetInterface` | IMetaDataImport QI ([PR #127028](#127028)) | | `GetMethodDefinitionByToken` | IXCLRDataModule — not yet implemented in cDAC | | `IsTrackedType` | GC heap analysis ([PR #125895](#125895)) | | `TraverseLoaderHeap` | Loader heap traversal ([PR #125129](#125129)) | **File-level allowlist:** | File | Reason | |------|--------| | `DacDbiImpl.cs` | Entire DBI/ICorDebug interface (122 methods) — deferred | ### Entrypoints.cs — Simplified creation Both `CreateSosInterface` and `CreateDacDbiInterface` now follow the same pattern: the legacy implementation is always passed through, and `LegacyFallbackHelper.CanFallback()` at each call site decides whether to delegate. Removed `prevent_release`, `noFallback` env var check, and null-legacy-ref logic. ### 13 Legacy wrapper files — Instrumented delegation sites All 296 delegation-only methods across all legacy wrapper files now call `LegacyFallbackHelper.CanFallback()`: - `SOSDacImpl.cs` (12 methods) - `SOSDacImpl.IXCLRDataProcess.cs` (38 methods, `Flush()` intentionally excluded — cache management) - `ClrDataModule.cs` (29 methods + IMetaDataImport QI) - `DacDbiImpl.cs` (122 methods) - Other wrappers: `ClrDataTask.cs`, `ClrDataExceptionState.cs`, `ClrDataFrame.cs`, `ClrDataValue.cs`, `ClrDataTypeInstance.cs`, `ClrDataMethodInstance.cs`, `ClrDataStackWalk.cs`, `ClrDataProcess.cs` ### CI Pipeline — `-noFallback` flag Updated `runtime-diag-job.yml` to accept a `noFallback` parameter that passes `-noFallback` to the diagnostics build script. The `cDAC_no_fallback` leg in `runtime-diagnostics.yml` now uses `noFallback: true` instead of setting `CDAC_NO_FALLBACK` as a pipeline-level environment variable. The `-noFallback` flag (from [dotnet/diagnostics#5806](dotnet/diagnostics#5806)) properly: - Sets `DOTNET_ENABLE_CDAC=1` and `CDAC_NO_FALLBACK=1` on the debugger process - Defines `CDAC_NO_FALLBACK_TESTING` to skip `ClrStack -i` tests (ICorDebug not implemented in cDAC) ### Stderr logging Every fallback attempt is logged to stderr in the format: ``` [cDAC] Allowed fallback: CreateStackWalk at DacDbiImpl.cs:590 [cDAC] Blocked fallback: SomeMethod at SOSDacImpl.cs:123 ``` The diagnostics test infrastructure (`ProcessRunner`) captures stderr and routes it to xunit test output with `STDERROR:` prefix, making fallback usage visible in test results. ## Test Results With `CDAC_NO_FALLBACK=1` and the current allowlist, running the full SOS test suite against a private runtime build: - **24 passed**, **2 failed** (flaky/pre-existing), **2 skipped** (Linux-only) - **0 blocked fallbacks** ## Motivation The existing cDAC test leg always has the legacy DAC as a fallback, so unimplemented APIs are silently handled. The granular no-fallback mode makes gaps visible per-method, helping track progress toward full cDAC coverage while keeping tests green for known-deferred APIs. --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Add a new
TestCDACNoFallbacktest configuration flag (SOS_TEST_CDAC_NO_FALLBACKenv var) that enables cDAC with no fallback to the legacy DAC.When enabled:
DOTNET_ENABLE_CDAC=1andCDAC_NO_FALLBACK=1on the debugger processCDAC_NO_FALLBACK_TESTINGdefine to skipClrStack -itests (ICorDebug is not implemented in the cDAC)TestCDACNoFallbacktakes precedence overTestCDACwhen both are setWraps
ClrStack -icommands with!IFDEF:CDAC_NO_FALLBACK_TESTING/ENDIF:CDAC_NO_FALLBACK_TESTINGin 7 script files.The
CDAC_NO_FALLBACKenvironment variable is added by dotnet/runtime#126752, which introduces the no-fallback mode to the cDAC runtime and adds a no-fallback test leg to the runtime-diagnostics pipeline.